Many conventional coaxial cables use braided copper wire to form a shield that isolates the cable from external electromagnetic radiation. The shielding also prevents leakage from the cable. The braided copper wire allows the cable to be flexible, but it also results in gaps in the shield layer that allow leakage and interference from external electromagnetic radiation. And, the inner dimension of the shield varies slightly because the braid cannot be flat. For better shield performance, some cables have a double-layer shield. This type of shielding may consist of two braids, but it is also common to have a thin metal foil shield covered by a copper wire braid. These shield designs often sacrifice flexibility for better performance and vice versa.
Additionally, these types of shieldings result in a cable with substantial weight. Heavier cables significantly increase transportation costs. For example, aircraft rely on many cables to carry a myriad of signals. Other forms of communication, such as radio frequency, simply cannot be used due to safety concerns. And, every pound of cable weight used on the aircraft increases the amount of fuel required to fly the aircraft. Similarly, heavier cables for ground use increase the fuel used by trucks to transport and lay the cable.